The Dark Souls team announced on the official Dark Souls Facebook page today that the Dark Souls II beta now has a planned start date. The first round of the beta will start on October 12th for North America and Europe, while the second round will start on the 27th. Registration for the beta is currently open via the official PlayStation Network Website. There is currently no word on when an Xbox 360 beta or PC beta will begin.
However, those of you in North America will be interested in this bit: According to Joystiq, the beta registrating isn't working yet for North American residents. Without a separate registration based on regions, it should open up to residents of the USA fairly soon.

Dark Souls II is planned for release in March 2014 for the PlayStation 3, Xbox 360 and PC. Developer From Software has not yet mentioned what the scope of the beta will be, but they have mentioned that participants who are selected to participate will receive further instructions once chosen.
Source: Dark Souls II Facebook